Membrane Unit, Housing Of A Pressure Measuring Unit And Pressure Measuring Unit

ABSTRACT

The present invention relates to a membrane unit adapted for use in a housing of a pressure measuring unit preferably for measuring pressure in an extra-corporal blood circuit comprising a flexible membrane and a fixing ring which is integral with the membrane so that the membrane and the fixing ring form a one-piece element, wherein the fixing ring has a lower flexibility than the membrane and wherein the fixing ring comprises fixing elements for fixing the fixing ring to the pressure measuring housing. The invention further relates to a housing as well as to a pressure measuring unit.

The present invention refers to a membrane unit adapted for use in ahousing of a pressure measuring unit which unit is preferably adapted tomeasure the pressure in an extra-corporeal blood circuit. Such pressuremeasuring units are usually referred to as “dome” or “pressure dome”.These units comprise a membrane forming one surface of a pressuremeasuring chamber which membrane in use is in contact with a fluid andwith a pressure transducer for converting pressures and pressure changesof the fluid into electrical signals.

A pressure measuring unit comprising a membrane and a housing is knownfrom U.S. Pat. No. 5,614,677. The pressure measuring unit disclosed inthis document comprises a housing comprising a pressure measuringchamber which is in fluid communication with an inlet and outlet of thehousing. One surface of the pressure measuring chamber is formed by amembrane which is fixed to the housing by means of a tension ringinserted in a groove on the upper surface of the housing. The tensionring is fixed in its position by aid of a guide of the transducer whichis abutting the upper surface of the housing.

Prior art document WO99/37983 also discloses a pressure measuring unitcomprising a housing with a pressure measuring chamber one surface ofwhich is formed by a membrane. The membrane comprises acircumferentially extending bead which is located on the side of themembrane facing the measuring chamber and which is pressed into a grooveof the housing. A similar arrangement is known from U.S. patentapplication US 2004/0050168 A1.

The pressure measuring units described in the prior art aredisadvantageous as the mounting of the membrane to the housing iscumbersome or has to be established by the membrane itself which is madeof soft material.

Accordingly, it is the object of the present invention to provide amembrane which can easily be fixed in a pressure measuring housing andat the same time exhibits good pressure transmitting and sealingproperties.

This object is solved by a membrane unit according to claim 1. Accordingto the invention a membrane unit is provided adapted to be inserted intoa housing of a pressure measuring unit preferably used for measuringpressure in an extra-corporeal blood circuit which membrane unitcomprises a flexible membrane and a fixing ring which is integral withthe membrane so that the membrane and the fixing ring form a one-pieceelement, wherein the fixing ring has a lower flexibility than themembrane and wherein the fixing ring comprises fixing elements forfixing the fixing ring to the housing. Accordingly, the membrane is partof a one-piece element composed of the membrane and a fixing ring havinga lower flexibility than the membrane. The invention ensures that themembrane is fixed reliably in the housing and thus reveals a goodpressure transmitting property to a transducer facing the membrane onthe other side than the fluid. Further a good sealing property of themembrane is obtained. A further advantage of the membrane unit accordingto the invention is that it can be easily mounted into the housing byengaging the fixing elements of the ring with the housing.

The fixing ring as well as the membrane can be connected to each otherby means of a suitable connection technique for example by means ofglueing or welding.

Alternatively, the fixing ring and the membrane can form a joint elementwhich is manufactured in a common process of manufacture. One example ofsuch a process is two-component injection moulding. Accordingly, themembrane unit can be manufactured as one part or can also bemanufactured as two elements which are linked to each other in a secondstep.

In a further embodiment of the invention the fixing elements of thefixing ring are formed as at least one projection, groove or thread.Alternative fixing elements are also conceivable.

The fixing elements of the fixing ring are located in a furtherembodiment of the invention at the outside portion of the fixing ring.Further the fixing ring may comprise a U-shaped portion and the fixingelements are located at one or both facing sides of the legs of theU-shaped portion.

The fixing ring may be arranged in a standing upright position on themembrane, preferably on the circumferential portion of the membrane.Preferably the ring extends perpendicularly relative to the membrane.

Furthermore, the circumferential portion of the membrane may have alarger thickness than the central portion of the membrane to improve thesealing properties.

In a further embodiment of the invention the membrane has acircumferential extending sealing lip for sealing the contact surfacebetween the membrane and the housing. The sealing lip is fixed in thecorrect position by means of the fixing ring which itself is fixed atthe housing.

In a further embodiment the sealing lip, in particular together with thepossible larger thickness portion in the circumferential portion of themembrane, extends into a first direction perpendicular relative to theplanar area defined by the central portion of the membrane whereas thering extends relative to this area into the opposite direction of saidfirst direction. In this embodiment, during use the fluid whose pressureis to be determined contacts the central portion of the membrane fromthe side of the first direction whereas the pressure transducer contactsthe membrane from the opposite site.

In another embodiment of the invention the membrane has a groove on thesurface facing the fixing ring for receiving a portion of the fixingring.

The contact surface between the membrane and the fixing ring may beprovided with one or more projections extending from one of the membraneor the fixing ring which engage with a groove in the other of themembrane and the fixing ring. The contact surface for example can beformed by a groove in the surface of the membrane facing the fixing ringwith the fixing ring being accommodated in this groove with its portionabutting the membrane.

In a further embodiment of the invention the shape of the sealing lip ofthe membrane equals the shape of the contact surface between themembrane and the fixing ring.

The present invention further refers to a housing of a pressuremeasuring unit which housing is adapted to receive a membrane unit, thehousing comprising an inlet and an outlet for a fluid, the pressure ofwhich is to be measured as well as a pressure measuring chamber being influid communication with the inlet and the outlet, wherein the pressuremeasuring chamber has an opening which is to be closed by a membranewhich is to be inserted into the housing, wherein the housing furthercomprises fixing elements for fixing a membrane unit, preferably amembrane unit according to one of claims 1 to 13, to the housing whereinthe fixing elements are located at one or more projections extendingaround said opening of the pressure measuring chamber.

The projection may extend perpendicularly relative to that surface ofthe pressure measuring chamber which is formed by a membrane, i.e.perpendicularly relative to the opening of the pressure measuringchamber which is to be closed by the membrane.

The projection may extend circumferentially around the longitudinal axisof the pressure measuring chamber which axis is perpendicular to saidopening of the pressure measuring chamber. In a preferred embodiment theprojection is located concentrically with the longitudinal axis of thepressure measuring chamber.

The fixing elements of the projection of the housing may be formed asgroove, jut or thread.

In a further embodiment of the invention the fixing elements are locatedon that side of the projection which is oriented to said opening of thepressure measuring chamber. The fixing elements may extendperpendicularly to the projection.

The invention is further directed to a pressure measuring unitcomprising a membrane unit according to one of claims 1 to 13 and ahousing according to one of claims 14 to 17, wherein the fixing elementsof the membrane unit engage with the fixing elements of the housing andwherein the membrane of the membrane unit forms one surface of thepressure measuring chamber of the housing.

Further details and advantages of the invention become apparent from anembodiment which is now described as an example by aid of the drawings:

FIG. 1 shows the pressure measuring unit according to the invention witha pressure transducer inserted therein,

FIG. 2,

FIG. 3 show in detail the fixing ring and the membrane in differentembodiments and

FIG. 4 shows the fixing ring and the membrane after and before assemblyaccording to FIG. 3.

FIG. 1 shows the housing 10 comprising an inlet 12 and an outlet 14 forconnection to an extra-corporeal blood circuit of a dialysis apparatus.Between the inlet 12 and the outlet 14 is located the pressure measuringchamber 16 which is in fluid communication with the inlet 12 and theoutlet 14. In this embodiment the pressure chamber 16 has a circularcross section when viewed from the top. The pressure measuring chamber16 is terminated at the top by the lower surface of a circular membrane20 which closes the upper opening 17 of the pressure measuring chamber16. At the edge of the membrane 20 there is a sealing lip 22 at thelower surface of the membrane 20 facing toward the housing 10 and agroove 24 on the upper surface of the membrane 20 facing a fixing ring30. The interior walls of the pressure measuring chamber 16 below themembrane 20 may have any shape suitable for the required purpose (e.g.rounded edges for blood compatibility, not shown in detail).

The membrane 20 and the fixing ring 30 form a one-piece element which isconnected after manufacture of both parts or which is manufactured in asingle process, for example by injection moulding.

The fixing ring 30 is made from a rigid material for guaranteeing theposition of the soft sealing membrane 20 after assembling. The membrane20 is made from elastic flexible material (for example thermoplasticelastomer, rubber) for sealing purposes as well as for transmitting thepressure/pressure changes to the transducer 100 abutting the uppersurface of the membrane 20.

The membrane 20 and the fixing ring 30 are in permanent contact witheach other and the contact surface 40 between both parts is not flat forproviding more surface for adhesion between the rigid material of thefixing ring 30 and the soft material of the membrane 20. In the presentembodiment the contact surface 40 comprises a projection 42 of thefixing ring 30 which engages with a groove 24 on the upper surface ofthe membrane 20 facing the fixing ring 30.

As further shown in FIG. 1 the fixing ring 30 at its outer surfacecomprises a radial projection 32 which is inserted into a correspondinggroove 19 on the inside of a cylindrical projection 18 of the housing10. The projection 18 extends perpendicularly to and circumferentiallyaround the membrane 20. At its inner surface the projection 18 comprisesthe circumferentially extending groove 19 in which as mentioned abovethe also circumferentially extending projection 32 of the fixing ring 30is inserted. The projection 18 and the fixing ring 30 are arrangedvertically, i.e. perpendicularly to the membrane 20.

The membrane unit consisting of membrane 20 and fixing ring 30 caneasily be inserted into the housing 10. Due to the presence of a rigidmaterial in form of the fixing ring 30 the desired position of thefixing ring 30 and of the membrane 20 is reliably established so that agood sealing property as well as a good pressure transmitting propertyof the membrane 20 are obtained. The membrane unit is easily connectedto the housing 10 by pushing the membrane unit from the top until theprojection 32 snaps into the groove 19. As both the fixing ring 30 andthe projection 18 are made of sufficiently rigid materials a firmconnection is achieved. At the same time the membrane 20 touches the rim25 of an opening 17 in the housing 10 that is to be closed by themembrane 20. Using appropriate sizes this contact can be used to apply acertain amount of tension to the membrane 20 upon fixing the ring 30 tothe housing 10. This tension may be advantageous for the pressuretransmitting properties for fluid pressures both below and above ambientpressure.

As the circumferential portion of the membrane 20 comprises a largerthickness portion 26 that is positioned in a groove 27 surrounding therim 25 of the housing 10 the membrane 20 is well sealed by thiscircumferential portion against the housing 10. The sealing is furthersupported by the sealing lip 22 that is pressed by the fixing ring 30into a complementary structure in the groove 27.

As shown in FIG. 1 the fixing ring 30 is joined perpendicularly to thecircumferential portion of the membrane 20.

In the shown embodiment the two parts are joined in a direction beingopposite to the direction the larger thickness portion 26 extendsrelative to the planar area defined by the central portion of themembrane 20.

FIGS. 2 and 3 show two different embodiments of the invention in whichthe contact surface 40 between the membrane 20 and the fixing ring 30differs. According to FIG. 2 the contact surface 40 differs in its shapefrom the shape of the sealing lip 22 and in the embodiment of FIG. 3 thecontact surface 40 as well as the sealing lip 22 have a similar oridentical shape.

As an alternative embodiment the fixing ring 30 may also have aninverted U-shaped upper portion so that it can be pushed over theprojection 18 of the housing 10. In this case fixing elements may beprovided on one or both of the legs of the U-shaped portion of thefixing ring 30.

In a further embodiment the fixing ring 30 and the projection 18 mayhave a thread or other suitable fixing elements.

FIG. 4 shows different views of the membrane unit composed of membrane20 and fixing ring 30. The embodiment of FIG. 4 corresponds to thatshown in FIG. 3. As may be gathered from FIG. 4 the membrane unit iscomposed of two parts which are linked to each other after manufacturethereof for example by glueing or welding. After the assembly thecomplete unit consisting of membrane 20 and fixing ring 30 is insertedinto the housing 10 shown in FIG. 1.

1: Membrane unit adapted for use in a housing (10) of a pressuremeasuring unit preferably for measuring pressure of blood in anextra-corporeal blood circuit, comprising a flexible membrane (20) and afixing ring (30) which is integral with the membrane (20) so that themembrane (20) and the fixing ring (30) form a one-piece element, whereinthe fixing ring (30) has a lower flexibility than the membrane (20) andwherein the fixing ring (30) comprises one or more fixing elements forfixing the fixing ring (30) to said housing (10). 2: Membrane unitaccording to claim 1, characterized in that the fixing ring (30) and themembrane (20) are linked to each other by means of a suitable connectiontechnique, preferably by means of glueing or welding. 3: Membrane unitaccording to claim 1, characterized in that the fixing ring (30) and themembrane (20) are manufactured jointly in a common process ofmanufacture. 4: Membrane unit according to claim 3, characterized inthat the fixing ring (30) and the membrane (20) are manufactured bymeans of two-component injection moulding. 5: Membrane unit according toclaim 1, characterized in that the fixing elements of the fixing ring(30) are formed as at least one projection (32), groove or thread. 6:Membrane unit according to claim 5, characterized in that the fixingelements of the fixing ring (30) are located at the outside area of thefixing ring (30) and/or that the fixing ring comprises a U-shapedportion, the fixing elements being located at one or both facing sidesof the legs of the U-shaped portion. 7: Membrane unit according to claim1, characterized in that the fixing ring (30) is joined perpendicular tothe membrane (20). 8: Membrane unit according to claim 1, characterizedin that the membrane (20) has a circumferential portion and a centralportion wherein the circumferential portion has a larger thickness thanthe central portion. 9: Membrane unit according to claim 1,characterized in that the membrane (20) has a circumferentiallyextending sealing lip (22) for sealing the contact surface between themembrane (20) and said housing (10). 10: Membrane unit according toclaim 8, characterized in that the sealing lip (22), preferably thesealing lip (22) together with a larger thickness portion in thecircumferential portion of the membrane (20) extends into a firstdirection perpendicular relative to the planar area defined by thecentral portion of the membrane (20) whereas the fixing ring (30)extends relative to this area into the opposite direction of said firstdirection. 11: Membrane unit according to claim 1, characterized in thatthe membrane (20) has a groove (24) on the surface facing the fixingring (30). 12: Membrane unit according to claim 1, characterized in thatthe contact surface (40) between the membrane (20) and the fixing ring(30) is not flat and is preferably provided with one or more projections(42) extending from one of the membrane or the fixing ring (30) whichengage with one or more grooves (24) in the other of the membrane (20)and the fixing ring. 13: Membrane unit according to claim 9,characterized in that the shape of the sealing lip (22) of the membrane(20) equals the shape of the contact surface (40) between the membrane(20) and the fixing ring (30). 14: Housing (10) of a pressure measuringunit, preferably for measuring pressure of blood in an extra-corporealblood circuit, comprising an inlet (12) and an outlet (14) for a fluidthe pressure of which is to be measured as well as a pressure measuringchamber (16) located in fluid communication with the inlet (12) and theoutlet (14), wherein the pressure measuring chamber (16) has an opening(17) which is to be closed by a membrane (20) which is to be insertedinto the housing (10), wherein the housing (10) further comprises fixingelements for fixing a membrane unit, preferably a membrane unitaccording to claim 1, to the housing (10) wherein the fixing elementsare located at one or more projections (18) extending around saidopening (17) of the pressure measuring chamber (16). 15: Housing (10)according to claim 14, characterized in that the projections (18) extendperpendicularly relative to said opening (17) of the pressure measuringchamber (16). 16: Housing (10) according to claim 12 characterized inthat the fixing elements of the projection (18) are formed as groove(19), jut or thread. 17: Housing (10) according to claim 14,characterized in that the fixing elements are located on that side ofthe projection (18) which is oriented to said opening (17) of thepressure measuring chamber (16). 18: Pressure measuring unit comprisinga membrane unit according to claim 1, wherein the fixing elements of themembrane unit engage with the fixing elements of the housing (10) andwherein the membrane (20) of the membrane unit forms one surface of thepressure measuring chamber (16) of the housing (10). 19: Pressuremeasuring unit comprising housing (10) according to claim 14, whereinthe fixing elements of the membrane unit engage with the fixing elementsof the housing (10) and wherein the membrane (20) of the membrane unitforms one surface of the pressure measuring chamber (16) of the housing(10).